Presently, minimally invasive imaging devices are employed in the diagnostic analysis of relatively large body cavities, such as, e.g., a heart chamber. Of particular interest to the present invention, ultrasonic imaging catheters have been employed to generate cross-sectional images from within the body cavity. The cross-sectional images reveal the surrounding contour of tissue, secondary structure, and other structural information relevant to treatment and diagnosis of various diseased conditions.
In this connection, a known imaging catheter 20, as depicted in FIG. 1, includes an elongate catheter body 22 with a distally formed elongate acoustic window 24 through which ultrasonic energy transparently passes. The catheter body 22 includes an imaging lumen 26 in which a rotatably and longitudinally translatable imaging core 28 is disposed. The imaging core 28 comprises a drive cable 30 along with a distally connected ultrasonic transducer housing 32 and mounted ultrasonic transducer 34. The transducer 34 is mechanically coupled to a drive unit (not shown) via the drive cable 30 and electrically coupled to a signal processor (not shown) via a transmission line 36 disposed in the drive cable 30. The transmission line 36 may consist of coaxial cable, triaxial cable, twisted pair, or other suitable configurations.
Disposal of the acoustic window 24, at a desired region within the body cavity and subsequent operation of the drive unit and signal processor, generates a longitudinal image scan of the tissue surrounding the body cavity. In particular, the electrical signals are transmitted to and received from the transducer 34, while the transducer 34 is rotationally and longitudinally translated relative to the acoustic window 24. In this manner, a multitude of imaging data "slices" are generated, which can be synthesized to produce a three-dimensional image of the body cavity for analysis by a viewing physician.
The ability to generate a three-dimensional image of a body cavity is advantageous in several respects. First, such an image generally allows a physician to ascertain the existence of a diseased region within the body cavity. Second, if such diseased region is found, the image permits a qualitative assessment of the nature of the disease in order to help select the most effective treatment modality. Third, the image can be used to determine the exact location of the diseased region, or the location of a therapeutic element relative to the diseased region, so that intervention can be directed only at the diseased region and not at healthy regions of the body cavity where the interventional procedure might cause damage.
Referring to FIG. 2, the imaging catheter 20 can be used to generate a three-dimensional image of a region of a heart 50. In particular, the imaging catheter 20 is advanced through the vasculature of the patient until the acoustic window 24 extends into a chamber of the heart 50, such as, e.g., the left ventricle 52. A longitudinal scan of the heart 50 is then performed, thereby generating a multitude of cross-sectional imaging data slices along respective imaging planes, such as, e.g., representative planes P(1)-P(5). Subsequent synthesis of the imaging data slices will result in a single three-dimensional image of heart tissue 50 which is intersected by the imaging planes. Heart tissue 50 not intersected by the imaging planes, such as, e.g., at the apex 54 of the heart 50, will not appear in the three-dimensional image. Thus, the image will not include potentially vital information that could lead to the proper diagnosis and subsequent treatment of a diseased region of the heart 50.
As shown in FIG. 3, the acoustic window 38 can be manipulated inside the heart 50, such that imaging planes of a subsequent longitudinal scan, such as, e.g., representative imaging planes P(6)-P(8), intersect heart tissue 50 not imaged during the first longitudinal scan, such as, e.g., at the apex 54. This task may sometimes be difficult or tedious to perform, and even if apparently successful, may result in a multitude of uncorrelated three-dimensional images, making proper examination of the heart 50 more difficult.
Further, referring back to FIG. 2, the force that the mitral valve 56 and entrance 58 to the left atrium 60 of the heart 50 exerts on the acoustic window 24 may create an arc 38 in the acoustic window 24 through which the heart 50 is imaged. As a result, the imaging data slices which are generated along the imaging planes, such as, e.g., planes P(4) and (P5), may, when synthesized, result in a image which is distorted at the left atrium 60 and right atrium 62, since the relative rotational orientation of the imaging planes P(4) and P(5) are unknown due to the randomness of the geometry of the arc 38.